An engine control system may sense engine intake manifold pressure to determine engine operating parameters that are a basis for adjusting engine actuators. For example, engine intake manifold pressure may be sampled to determine engine intake manifold absolute pressure (MAP). The engine intake manifold pressure along with engine speed may be converted into an amount of air flowing through the engine using the ideal gas law. Once engine air flow is known, a desired amount of fuel that provides a desired engine air-fuel ratio may be determined by dividing the engine air flow rate by the desired engine air-fuel ratio. However, the engine intake manifold pressure may include frequencies that may cause intake manifold pressure to exhibit a standard deviation that is larger than desired. If the engine fuel amount were adjusted responsive to the raw (e.g., unfiltered) engine intake manifold pressure sampled at a slow rate and at fixed crankshaft intervals, the engine's air-fuel ratio may vary more than is desired.
One way to reduce engine air-fuel variation is to apply a first order low pass filter to a MAP signal and sample the MAP signal at a rate that is an integer multiple of engine firing frequency. The filtered MAP may then be used to determine an amount of fuel to inject to the engine. However, if the engine has a capacity to deactivate and reactivate individual cylinders such that the actual total number of active cylinders changes from engine cycle to engine cycle, processing the MAP sensor signal via a first order low pass filter and a constant sampling frequency may not provide a filtered MAP sensor signal that is suitable for controlling engine fuel injection because frequencies within the MAP sensor signal dynamically change while poles of the first order filter remain constant.
The inventors herein have recognized the above-mentioned issues and have developed an engine operating method, comprising: receiving a signal to a controller; adjusting coefficients of a finite impulse response filter responsive to an engine induction ratio (e.g., an actual total number of active cylinders in a cylinder cycle (cylinders that are combusting air and fuel) divided by the actual total number of engine cylinders); filtering the signal via the finite impulse response filter; and adjusting one or actuators responsive to the filtered signal.
By adjusting coefficients of a finite impulse response filter or an infinite impulse response filter responsive to engine induction ratio, it may be possible to provide the technical result of providing a filtered engine signal that has a desired level of dynamic response with a desired standard deviation even when an engine is operated with an induction ratio that is less than one. When an engine signal is filtered according to the present description, the filtered engine signal may have a desired standard deviation that allows engine air-fuel ratio to be tightly controlled. Further, other engine actuators, such as camshafts and intake throttles, may be more precisely controlled when the engine induction ratio changes or is a fractional value. The finite impulse response filter may be implemented via instructions in a controller so that modification of filter coefficients may be synchronized with cylinder mode changes.
The present description may provide several advantages. Specifically, the approach may improve engine air-fuel control. Further, the approach may be applied to a variety of different engines having different cylinder configurations. Further still, the approach may eliminate or reduce signal strength of frequencies of a signal that tend to increase a standard deviation of the signal so that actuators that are adjusted responsive to the signal may be smoothly controlled while providing a desired dynamic response.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.